Burner control apparatus



June 28, 1966 R. w. BROWN 3,258,055

BURNER CONTROL APPARATUS Filed Sept. 1, 1965 Is\ l4 H 25 12 2e 28 AC. LINE 3O 29 TO BURNER l7 l8 l5\ H STACK MOUNTED a6 BIMETAL FLAME THERMISTOR DETECTOR INVENTOR RICHARD W. BROWN M A TORNEY United States Patent 3,258,055 BURNER CONTROL APPARATUS Richard W. Brown, Excelsior, Minn., assignor to Honey,-

well Inc, Minneapolis, Minn., a corporation of Dela- My invention is concerned with an improved burner control apparatus and more particularly with a burner control apparatus utilizing a thermistor to shunt the normally open contact of a flame detector and to thereby pro vide the control of a burner control relay such that the switches of the flame detector need not be of the overlapping type, and such that a flame failure is effective to cause a recycle of the burner control relay since the relay will not remain energized through the cold thermistor.

The accompanying drawing is a single diagrammatic figure of the control apparatus.

Referring to the single figure, reference numeral 19 designates a controller which may be a room thermostat located in an area heated by an associated fuel burner unit, not shown. The fuel burner unit is adapted to be energized by a burner control relay 11 having an actuating winding 12 and normally open switches 13 and 14. Switch 14 is connected to the burner to energize the burner upon closing of this switch.

Reference numeral 15 designates a flame detector, for example a stack mounted bimetal flame detector having a bimetal element 16, a normally closed switch 17 and a normally open switch 18. Upon heating of 'bimetal 16 by the presence of flame at the fuel burner unit, switch 17 first opens and thereafter switch 18 closes. Subsequently, upon cooling of bime-tal 16, switch 18 first opens and then switch 17 closes. Thus, switches 1'7 and 18 are of the non-overlapping type.

Reference numeral. 19 designates a safety cutout means in the form of a bimetal operated safety switch having a normally-closed switch 20, a bimetal 21, and an actuating heater 22. After a time period of energiza-tion of heater 22, bimetal 21 warps to the right and releases switch 2% to an open position. Manual'reset means may be provided to reset safety cutout means 19 to the closed position as shown.

Operating voltage for my improved burner control apparatus may be provided by a transformer 25 having a primary winding 26 adapted to be connected to a source of A.C. voltage, and having a secondary winding 27 with end terminals 28 and 29 and a tap 30.

In order to avoid the necessity of having overlapping contacts for the flame detecting means, I provide a thermistor 31 which is connected in parallel with the normally open switch 18 of flame detecting means 15.

The apparatus of my invention can be considered to be three circuit configurations in which three circuits are connected between the power supply terminals 28, 29 and 30 and a further terminal 32. The first of these circuits is connected from terminal 28 through the winding of relay 11 and thermistor 31 to terminal 32. Th second of these circuits is connected through an impedance in the form of heater 22 and through normally closed switch 17 of the flame detecting means to terminal 32. The third of these circuits is connected from terminal 30 through normally open switch 13 of relay 11 to terminal 32.

My invention may provide a circuit configuration whereby controller 10 and safety cutout means 19 are located in different portions of the burner control apparatus than shown, for example, in th line "voltage side of transformer 25. The essential feature is that the closing of controller 19 is effective to energize the winding of relay 11 only if switch 20 of safety cutout means 19 is closed.

Upon closing of controller 10, a circuit is established from tap 28 through winding 12, thermistor 31, the normally closed switch 17 of flame detecting means 15, and heater 22 to terminal 29. The voltage present in this circuit is the relatively high voltage existing across terminals 28 and 29 of secondary winding 27, the two portions of the secondary winding being in voltage aiding relation. As a result of this circuit, insufficient current flow through the then cold thermistor 31 to operatively energize winding 12 of the relay. However, after a short time period, thermistor 31 self heats, its impedance lowers, and relay Winding 12 is operatively energized by the higher magnitude current.

The closing of relay switch 14 is effective to energize a burner to attempt to establish flame.

The closing of switch 13 is effective to complete an energizing circuit for heater 22 of safety cutout means 19 and connects this heater across the source of voltage 29- 3-3, under the control of the normally closed switch 17 of the flame detecting means.

The closing of switch 13 is also effective to connect terminal 32 to transformer terminal 30. Thus, the wind- .ing of relay 11 is energized from the source 28, 30 through the now hot and low impedance thermistor 31. This low impedance allows sufficient current to flow through the winding of relay 11 to maintain the winding operatively energized.

Upon flame being detected flame detecting means 15 is first effective to open switch 17. This is effective to de-energize heater 22 of safety cutout means 19. Shortly thereafter, switch 18 closes to form a shunt circuit around thermistor 31. This is the running condition of the apparatus.

If a flame failure is subsequently experienced, switch 18 opens and the now cold thermistor 31 is immediately inserted in series with winding 12 across the voltage source .28, 31). The magnitude ofcurrent now flowing through Winding 12 from source 28, 30, with thermistor 31 cold, is such as to operatively de-energize the winding and switches 13 and 14 open. The apparatus then recycles when switch 17 closes upon further cooling of bimetal 16.

I claim as my invention:

1. Burner control apparatus having terminals which can be characterized as terminals a, b, c and d, terminals a and 1) being adapted to be connected to a source of voltage, and terminals [2 and c being adapted to be connected in aiding relation to a further source of voltage, the apparatus comprising:

impedance means,

relay means having an electrical actuator and normally open switch means,

flame detecting means having normally closed switch means and normally open switch means, a negative temperature coefficient impedance element, first circuit means connecting said impedance means and said flame detecting means normally closed switch means in series between terminals a and d,

second circuit means connecting said relay means actuator and said flame detecting means normally open switch means in series between terminals c and d,

third circuit means connecting said relay means normally open switch means between terminals b and d,

and fourth circuit means connecting said impedance element in parallel with said flame detecting means normally open switch means.

2. Burner control apparatus as defined in claim 1 wherein said impedance means is the electrical actuator of a time delayed safety cutout means.

type.

3. Burner control apparatus as defined in claim 1 wherein the normally open and normally closed switch means of said flame detecting means are of a non-overlap 4. Burner control apparatus as defined in claim 1 wherein the impedance element is a thermistor which operates in a self-heating mode so long as said flame detecting means normally open switch means is open.

5. Burner control apparatus as defined in claim 1 wherein said impedance means is the electrical actuator of a time delayed safety cutout means, wherein the normally open and normally closed switch means of said flame detecting means are of a non-overlap type, and wherein the impedance element is a thermistor which operates in a self-heating mode so long as said flame detecting means normally open switch means is open.

6. Burner control apparatus, comprising:

a relay having an actuator and a normally open switch,

flame detecting means includes a normally closed switch and a normally open switch, a thermistor, first circuit means for said actuator including said thermistor and the normally closed switch of said flame detecting means, second circuit means for said actuator including said thermistor and the normally open switch of said relay, and circuit means connecting the normally open switch of said flame detecting means in parallel with said thermistor. 7.'Burner control apparatus as defined in claim 6 wherein said first circuit means includes a first voltage source having a series impedance means, and said second circuit means includes a second voltage source of a lower voltage than said first voltage source.

References Cited by the Examiner UNITED STATES PATENTS 2,086,823 7/1937 Shaw 158-28 2,672,188 3/1954 Cassidy 158-28 3,049,169 8/1962 Bredesen et al. 158-28 JAMES W. WESTHAVER, Primary Examiner. 

1. BURNER CONTROL APPARATUS HAVING TERMINALS WHICH CAN BE CHARACTERIZED AS TERMINALS "A," "B," "C" AND "D," TERMINALS "A" AND "B" BEING ADAPTED TO BE CONNECTED TO A SOURCE OF VOLTAGE, AND TERMINALS "B" AND "C" BEING ADAPTED TO BE CONNECTED IN AIDING RELATION TO A FURTHER SOURCE OF VOLTAGE, THE APPARATUS COMPRISING: IMPEDANCE MEANS, RELAY MEANS HAVING AN ELECTRICAL ACTUATOR AND NORMALLY OPEN SWITCH MEANS, FLAME DETECTING MEANS HAVING NORMALLY CLOSED SWITCH MEANS AND NORMALLY OPEN SWITCH MEANS, A NEGATIVE TEMPERATURE COEFFICIENT INPEDANCE ELEMENT, FIRST CIRCUIT MEANS CONNECTING SAID IMPEDANCE MEANS AND SAID FLAME DETECTING MEANS NORMALLY CLOSED 